1. Field of the Invention
This invention relates to the field of power plants. More particularly, the present invention relates to devices and methods used in the field of heat engines for various applications including mechanical drives. Embodiments of the present invention provide subsonic and stationary ramjet engines.
2. Description of the Related Art
To conserve fossil fuels and reduce the worldwide production of carbon dioxide, CO2, the most effective method is to increase the efficiency of automobile engines and other fuel burning engines. The efficiency of the average automobile engine on the road in the United States is approximately 21%. An automobile engine with 21% efficiency burns three times as much fuel as an automobile engine with 63% efficiency. Ramjet engines possess 63% efficiency and higher.
Ramjet engines have been around for 50 years, and are famous for high efficiency, yet, today, ramjets have virtually no commercial applications other than military. There are reasons for that. Supersonic speed generates shockwaves and shockwaves waste energy. Unless an aircraft flies at very high altitude where air is much less dense, it will consume a great deal of fuel by flying supersonically. So there is little economic demand for commercial supersonic aircraft. But there is some demand, and it is not being met by ramjet engines even though they are much more efficient than turbine engines.
The words supersonic and subsonic usually refer to speed of sound in the ambient atmosphere. Inside the apparatus of this invention speed of sound changes with temperature, and the words supersonic and subsonic usually refer to local speed of sound in the air or gas under those conditions. The speed of sound can vary by a factor of two in the same air or gas traveling through the apparatus. Mach speeds almost all refer to speed of sound in the atmosphere.
Ramjets use de Laval nozzles to convert supersonic speed air to subsonic and vice versa with the flow reversed in the nozzle. De Laval nozzles are highly efficient devices known for over a century. An input de Laval nozzle slows down supersonic air by reducing the area of a tube containing the flow to what is known as the choke area, where the air reaches local speed of sound. Beyond the choke area the nozzle increases the area of flow to further slow down the air. The faster the nozzle moves through the air, the more air can pass through the same choke area, because the high kinetic energy of the air relative to the nozzle is converted into higher temperature and higher density in a de Laval nozzle. But, for each airspeed, the rate at which air can pass through the choke area is fixed. The choke area regulates the rate of flow at every energy level of the air. There is a choke area in the input nozzle to the ramjet engine and there is a choke area in the output nozzle from the engine. Both of these areas regulate the rate of flow of air/gas. And that is a problem. They have to be coordinated—at supersonic speed. It is not impossible, but it is very difficult. If an output subsonic to supersonic de Laval nozzle does not receive enough flow, it will not make the isentropic conversion to supersonic, and thrust from the exhaust is reduced. If it receives too much flow, some gas is pushed back, making the pressure in the combustion chamber go up. If the pressure in the combustion chamber goes up, the front or input de Laval nozzle gets backed up.
Another problem with ramjet engines is that they only work at supersonic speeds. A ramjet engine cannot be used inside an ordinary room, because flying at supersonic speed requires faster turns than the engine can survive, even if it is held by a very long arm. Stationary testing of ramjet engines is possible, in a supersonic wind tunnel, but that is not a practical way to get mechanical power from the ramjet engine. Further, the use of paired de Laval nozzles is one limiting factor keeping ramjet engines from being more widely used in aircraft.